After looking at your attached web sites, i did a calculator on my tyre size and i think you will find i have it right as it's within 0.2% @60 mph..so at 59.99 mph i will have a reading of 60 mph and we all no speedos are not that accurate anyhow.
I do believe the 235 on the front reduce the risk of tramlining too over all the package i have feels very well set up...i would recommend rethinking rolling the arches as this would be a costly venture to reverse once carried out and it will also act as a rust trap.
I do understand we all like our car's to look the way we love em to look, if that makes sense...just be careful you don't ruin it..have a look on the forum i remember looking at a post once where a guy had put 295's on[sHOCK][/sHOCK] imho i didn't look too good...but hey that just my opinion.
If your looking to get good grip think quality tyre not width....or if your just going on just looks then go on what you love the look of, but as you said the ride can be compromised.
Hope i have at least given you some idea's of what to think about and i have not come across too harsh...good luck:)
have a look here..
http://www.mkivsupra.net/vbb/showthread.php?t=143818&highlight=295