I can't say I've noticed a deficit in steering response running a 55 rather than 50 sidewall on my 19s (255/55/19 instead of the OEM 255/50/19). And that's with ATs rather than pure road tyres. I hate to think how hard/fast I'd have to be driving the thing to make it feel like it wasn't turning in properly. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

"I did however re-calibrate the suspension to lower the ride height slightly to compensate for the slight increase in height on fitting the 45 profile tyre and 21" rims".

I did not change the vehicle CCF file when changing the tyres to the higher profile. The vehicle pitches from side to side quite noticeably (and quite uncomfortably) with the higher profile tyres.

That was with the 21" rims, never changed anything with the 20" 45 profile and it still had no effect on the handling, just improved the ride comfort slightly and made the speedo a little more exact. I did play about with different wheel/tyre size settings in the CCF and it made no noticeable difference to anything so left it as it was when it left the factory. The car I fitted the 21" rims to also has the CVD system fitted, but I wouldn't know if that would make any difference to the handling with the large wheel/tyre combination.

Cheers
Col