Wheel size confusion

[Technomad]

I'm looking for a set of winter wheels for my 997.2 C2S. Standard wheel sizes are 8J19 ET57 front/11J19 ET67 rear and I'd prefer to stick with 19" wheels rather than drop to 18" What's confusing me is the suitability of e.g. BBS CH-Rs, which are 8.5" at the front and with offsets of ET51/56 (f/r). I'd have thought that the offset should be pretty damn consistent between wheels for a given model (although I note that Porsche themselves aren't consistent on this). So thoughts and advice on the CH-Rs versus getting a (slightly boring) set of OEM winter wheels/tyres?

Richard

[Technomad]

As I live 70 miles from the nearest OPC and mobile tyre fitters don't come out here (I've tried) I prefer to keep winter wheels for all our cars and have them swapped over by the local garage - I don't like the idea of having too many tyres swaps done given the potential for damage to the wheels. My other concern about the OEM 18" winters is that they're notably narrower at the rear (265 vs 295) so on those not infrequent winter days when a good blast is entirely possible, I'd find grip limited by the narrower tyres (something I've found with my 123D)