There is a few technical differences between the 26p and 25p besides the £130 price increase. From what i've read the 26p has slightly better cooling and can enable you to use a slower fan speed, thus reducing noise, the most important factor to me when doing webmaster work.
Going to order this tomorrow:
FS-059-SH Shuttle XPC SN26P Aluminium Barebones System - AMD 64 (Socket 939) (FS-059-SH)
£339.95 £339.95
MY-057-OC OCZ 2GB (2 x 1GB) PC3200 Dual Channel Platinum Series EL-DDR CAS2 (OCZ4002048ELDCPE-K) (MY-057-OC)
£124.95 £124.95
CD-033-LG LG GSA-4167BAL 16x16 DVD±RW Dual Layer ReWriter (Black) - OEM (CD-033-LG)
£22.95 £22.95
OS-001-MS Microsoft Windows XP Home Edition inc. SP2 - OEM - 1Pk (N09-01528) (OS-001-MS)
£49.95 £49.95
SW-017-NO Symantec Norton Internet Security Suite 2006 - OEM (SW-017-NO)
£19.95 £19.95
CP-148-AM AMD Opteron UP 170 Dual Core San Diego 2.0GHz 2MB Cache (Socket 939) - Retail (CP-148-AM)
£274.95 £274.95
GX-009-BG BFG GeForce 7800 GTX OC 256MB GDDR3 VIVO TV-Out/Dual DVI (PCI-Express) - Retail (GX-009-BG)
£269.95 £269.95
AC-000-AC Arctic Silver 5 Thermal Compound (3.5g) (AC-000-AC)
£2.95 £2.95
Subtotal £1,105.60
VAT £193.48
Total £1,299.08
I've read good comments on a few forums about the low noise level of the BFG GeForce 7800 GTX.