I can't really comment too much on the ride other than to say that fitment of the spacers to mine hasn't been detrimental to the handling or ride. Im theory, with spacers fitted, you're driving on a wider wheelbase so the handling could be improved. Although I'm sure there are others on here with a different school of thought.
I think the 20's on the rear look great, and would probably say I'd go to 25 if I could find someone who makes them!! That said, I'm not sure how well 25's would fit on a car with lower offset alloys. My 18" style 269's are a relatively high offset which gives for a flatter face and thus doesn't get too close to the body work at the top of wheel. However, I have read that plenty of guys have put 20mm spacers on pre-LCI motors with standard wheels with no problems at all.
If I was you I'd stick the 20s on the back and get the 10s back on the front. That should even it up a bit and give a great look!
I will try to get some pics up for you ASAP. Might not be until after the weekend but I will do my best.
Hope that helps.
2006 E90 325i SE - Silver - Manual - Xenon Headlights - Full Leather Interior - Extended Interior Light Package - DCC - 18" Black Multispoke Alloys ~ Style 269.