Found some more - Boxster S and 993/996 Turbo:
piston size/area
1. stock front caliper:
Golf/GTI - Ate FN3 54 mm caliper: 2290 mm²
S3/R32/R - FNRG 57 mm: 2552 mm²
2. aftermarket - proper match:
AP Racing 6-pot CP7068-00 (355x32 ) > 2350 mm²
Boxster: 40 mm + 36 mm > 1257 mm² + 1018 mm² = 2275 mm²
Boxster S: 40 mm + 36 mm > 1257 mm² + 1018 mm² = 2275 mm²
993 Turbo: 36 + 44 mm > 1018 mm² + + 1520 mm² = 2538 mm² (on the edge)
Brembo GT 'A-caliper': 40 mm + 36 mm > 1257 mm² + 1018 mm² = 2275 mm²
Stoptech ST-40: 38 mm + 34 mm > 908 mm² + 1134 mm² = 2043 mm²
3. aftermarket - poor match:
Forge: 707 mm² + 1046 mm² + 1164 mm² = 2917 mm²
996 Turbo: 40 + 44 mm > 1257 mm² + 1520 mm² = 2777 mm²
Q7/Touareg/Cayenne (three variants):
34/36/38 mm : 907.920 + 1017.876 + 1134.115 = ~ 3060 mm²
32/36/38 mm : 804.248 + 1017.876 + 1134.115 = ~ 2956 mm²
30/34/38 mm : 706.858 + 907.920 + 1134.115 = ~ 2749 mm²
4. master cylinder diameter:
- 22,22 mm > 388 mm² (some Mk.V GTI, Mk.V + Mk.VI Golf)
- 23,81 mm > 445 mm² (Mk.V R32, Mk.V GTI, Mk.VI GTI, Golf R)
- 25,40 mm > 507 mm² (RS3 + TT-RS)
If you know the piston diameter: Pi * radius² = area