5-lug x 4.5" bolt circle has been a common trailer pattern for a long time
boat and utility trailers have used it almost exclusively
many boat trailer manufacturers are now using the same pattern w/ fancy(charging the customer $$$) aluminium wheels
those aluminium wheels are not uncommon in our area on CraigsList
using an off sized spare is only an issue if your trailer drags w/ the smaller wheel installed OR the tire isn't rated for highway speeds
yes the bearings will run faster butt if you keep your bearing maintenance up to date/par there should be no issue there
the ony time when running different sized tire/wheel combinations is really important is on the TV drive axle and even then for a short distance at slow speeds it doesn't usually cause any problems unless your TV has a Limited slip differential
some types of race cars mount substantially different sizes on the same axle w/o problems
for the average trailer tower the OP's ponderment shouldn't be an issue
just find a wheel/tire combination w/ the correct bolt patter and the largest diameter that will fit between the frame rails and mount it under the body
piece o' cake
sw