@Mike
Here some of my observations of the various kits - bare in mind I thought about this for 18 months before committing to the Reyland kit.
I actually ordered but then cancelled both the Essex AP Racing Sprint kit and the Godspeed AP kit, before settling on the Reyland kit, this was after speaking with @Ade and one of the technical team at AP Racing.
These are for the approx 330mm kits (355mm+ kits have different requirements)
Reyland - AP Kit:
Pro's:
AP Caliper - CP9200 (2 piece aluminum body)
4 Pistons
Dust Boots - Made by Brembo
Perfect for Street and track
Common Pad Size
330mm x 28mm discs - 2 piece
Good thermal capacity
High quality caliper by premium brake manufacturer.
Keeps stock brake bias
Complete kit - Calipers, Pads, Brake lines, brackets, discs
Various disc options - Either bolted or floating brake disc hat/bell. AP or Reyland disc's.
Clear's the majority of 17" wheels
Latest design of caliper by AP Racing - including new paint finish
Used by various members of the community - with extensive track use
Con's:
Reasonably expensive
Custom made brackets, which you need to shim to get perfect fitment
Won't fit under stock wheels without spacer.
Godspeed - Brembo's:
Pro's:
Brembo caliper
4 piston
Dust boots
330 x 28 discs
2 piece discs
Cheap
Con's:
Unknown caliper model
Unknown caliper material
Unknown piston sizes - not sure what effect this will have on brake bias
Unknown pad size
No brake lines included
Godspeed - AP Kit:
Pro's:
AP Caliper - CP9040 (2 piece aluminum body)
Dust Boots - Made by Brembo
Common Pad Size
Good thermal capacity
High quality caliper by premium brake manufacturer.
Latest design of caliper by AP Racing - including new paint finish
Con's
Reasonably expensive
Caliper designed for a 362mm disc - not 330mm as included
Caliper designed for a 32mm thick disc - not 30mm as included
Ø330mm disc in this caliper will leave a fairly large gap between the discs OD and the calipers disc pathway and this gap can be prone to collecting road debris.
6 pistons - overkill
No brake lines included
K-Sport:
Pro's:
Cheap
Used by various members of the community - with extensive track use
Clear's the majority of 17" wheels
Complete kit - Calipers, Pads, Brake lines, brackets, discs
330mm x 32mm? disc - 2 piece
Dust boots
Perfect for Street and track
Con's
8 pistons
Unknown piston sizes - not sure what effect this will have on brake bias
Unknown pad size
Unknown replacement disc price
Won't fit under stock wheels without spacer.
STi Brembo's - Used on Subaru Impreza WRX STi:
Pro's:
Cheap
Used by various members of the community - with extensive track use
Clear's the majority of 17" wheels
Complete kit - Calipers, Pads, Brake lines, brackets, discs
326mm x 30mm disc
Various disc options
Common pad size
Dust boots
4 pistons
Con's
Shifts brake bias forward massively
Steel calipers - heavy
Bleed nipples need swapping - i.e. caliper refurb before fitment
Not a complete kit
Won't fit under stock wheels without spacer.
Only available second hand
RR Racing (Wilwood😞
Pro's:
Cheap
Wilwood caliper
Complete kit - Calipers, Pads, Brake lines, brackets, discs
326mm x 30mm disc - STi disc's so cheap replacements
Clear's the majority of 17" wheels
Con's
6 pistons
no dust boots
Won't fit under stock wheels without spacer.
Limited pad selection
Only available from the US
Moves brake bias forward
Essex Parts - AP Racing Sprint Kit:
Pro's:
AP Caliper - CP8350
4 Pistons
Perfect for Track Use
Common Pad Size
2 piece discs
Extremely light
High quality caliper by premium brake manufacturer.
Complete kit - Calipers, Pads, Brake lines, brackets, discs
Clear's the majority of 17" wheels
Keeps stock brake bias
Used by various members of the community - with extensive track use
Con's:
Expensive
299x32mm disc's - Can have some thermal issues
Only available from the US
Won't fit under stock wheels without spacer.
No dust boots
Not a daily driver friendly caliper
AP Racing Genuine kit:
Pro's:
AP Caliper - CP6600 (2 piece aluminum body)
4 Pistons
Dust Boots
Perfect for Street and track
Keeps stock brake bias
Complete kit - Calipers, Pads, Brake lines, brackets, discs
Clear's the majority of 17" wheels - including stock wheels
Con's:
Very Expensive
26mm thick discs
Limited pad options
Limited disc options
Uses older AP caliper
Stoptech ST40:
Pro's:
Stoptech ST40 caliper
4 Pistons
Clear's the majority of 17" wheels
Complete kit - Calipers, Pads, Brake lines, brackets, discs
328mm x 28mm disc - 2 piece
Dust boots
Perfect for Street and track
Con's
Expensive
Can't 100% confirm piston sizes
Limited pad replacement options
Unknown replacement disc cost
Won't fit under stock wheels without spacer.