UCF Caliper Clearance

I have a 99 LS400 w/ the biggest calipers the UCF1x or 2x came with (I believe). Is it going to hurt my braking performance to downgrade to a smaller, older model caliper and if I did this would I even get the 5mm of clearance I need? I'll most likely just use a slip on spacer but I think it's kinda lame just for 5mm of clearance... any other options?

Get a set of rims made for backspacing or x factor in clearance.
Also a spacer works fine as i have on mine.

Im pretty sure youll be able to get more then 5mm of clearance with ucf1x brakes.

I know I can most likely run the wheels with the smaller brakes, I'm just trying to decide what the best method is... they're 10+13 fronts and they do clear UFC1x, I just need a small bit more on my 99