i would say, from the fun point of view, the 4.6 was a raw beast (not an M3 or E39 M5), it still felt a bit heavy but in my opinion was quicker to take off, and the 4.8 is a little more refined beast (it says on paper it is faster to take off, but it does not feel so)...

I went with the top of the line (the "iS") because i HATE retrofitting and those beasts had so many items standard that the retrofitting was minimal... as a matter of fact, the only retrofits the 4.8 got, was the TV module, rear camera, aspheric mirror, first aid kit, fire extinguisher, TV Switch and the TV AV in/out modules, AUX input... the mods included headrest monitors, 2 x 110 VAC converters under the front seats, blacked out badges on everything except for the engine cover and the keyfob, power distribution for the aftermarket mods via Wake-on-LAN signal...
I did not have to worry about rear seat heaters, silver gauges on the dash, nav system, sport seats, etc - they were already part of the car...

so, for me - being lazy was a deciding factor... lol... but, i strongly believe that laziness moves human progress - if we were not lazy, we would still get up to change the channel on a TV!!!!