Got this from a HK site. Not sure if accurate as I personnally dont have a RX7. Hope this helps.

FD3S I A-tune___twin turbo tuning; 350hp; strong on dry; gd accel.; powerful in each gear
FD3S I B-tune___big hp single turbo tuning; average performance; weak below 5500 rpm (has turbo lag especially braking 2 much); Protection Frame installed
FD3S I C-tune___twin turbo tuning; gd steering performance; 'not bad' accel. ability; stable on wet
FD3S I D-tune___twin turbo tuning; powerful start-up and strong accel. performance; unstable; little drift in high speed
FD3S VI A-tune___twin turbo tuning; strong on dry; gd accel
FD3S VI B-tune___twin turbo tuning; stable on wet; gd steering
[FD3S I]
Wheels(15000 pts)
Mazdaspeed gold star wheels (D-tune)___understeering; light weight
Mazdaspeed silver star wheels
*Mazdaspeed black wheels (A-tune)___average performance; super steering performance on dry(grip)
Mazdaspeed white wheels
REÓêŒm gold wheels (B-tune)___stable; gd for rain battle
REÓêŒm silver wheels (C-tune)__same as gold wheels; light weight
Mazda original wheels
Wing(60000 pts)
*Mazdaspeed Wing(A-tune)___stable; light weight; better accel., average performance
Mazda Wing(B-tune)___nimble for hairpin; light weight; better accel.
*REÓêŒm Double-Deck Wing(C-tune)__stable; grip; heavy weight; gd for high speed track(myogi, usui)
Mazdaspeed GT Wing(D-tune)___unstable; super light weight
Mazda original spoiler(N-tune)
Muffler(5000 pts)
¸ß˜ò†¢½é Muffler(A-tune)___strong accel.; less stable; little understeering
ÑҞ|¹§×Ó Muffler(B-tune)
REÓêŒm Muffler(C-tune)
*Mazdaspeed Muffler(D-tune)___stable; powerful start-up; strong accel.
Mazda original double-muffler
Head Cover(40000 pts)
Mazda original head cover (N-tune / A-tune)
ÑҞ|¹§×ÓHead Cover(B-tune)
REÓêŒm Head Cover(C-tune)
Mazdaspeed Head Cover(D-tune)
Side Mirrors(10000 pts)
Mazda original side mirrors(N-tune / A-tune / C-tune / D-tune)
ÑҞ|¹§×Ó bullet side mirrors(B-tune)
Stickers(5000 pts)
RedSuns Stickers
[FD3S VI]
Wheels(15000 pts)
Mazdaspeed gold star wheels
Mazdaspeed silver star wheels
*Mazdaspeed black wheels(A-tune)
Mazdaspeed white wheels
REÓêŒm gold wheels
REÓêŒm silver wheels(B-tune)
Mazda original wheels____very drift
Wing(60000pts)
*Mazdaspeed GT Wing(A-tune)___light weight; powerful start-up
Fujita engineering Double-Deck GT Wing(B-tune)__stable; grip; heavy weight; gd for high speed track
Mazda original wing(N-tune)
Muffler(5000pts)
Mazdaspeed Muffler(A-tune)____start-up faster than B-tune Muffler
*Fujita engineering Muffler(B-tune)____better accel. than A-tune Muffler
Mazda original double-muffler
Head Cover(40000pts)
Mazda original head cover(N-tune)
Mazdaspeed Head Cover(A-tune)___average performance
*Fujita Engineering Weight Reduction Head Cover(B-tune)___average performance
Side Mirrors(10000pts)
Mazda original side mirrors(N-tune)
Mazdaspeed Bullet Side Mirrors(A-tune)
Fujita engineering Bullet Side Mirrors(B-tune)
*Strongly recommend
FD I B tune Wing = FD VI N tune Wing (Mazda)
FD I D tune Wing = FD VI A tune Wing (MazdaSpeed)
FD I D tune Head Cover = FD VI A tune Head Cover (MazdaSpeed)
FD I A tune Wheels = FD VI A tune Wheels (MaxdaSpeed)