regarding you ramps you need to measure clearance for 5" pipe you will need close to 6" clearance. As for blowing out it takes a little longer "more volume to fill" as for thicker slurry I think it will blow out easier than 4". Performance wise you won't be disappointed with 5" pipe. We have two compressors to blow out and send a sponge every time.
What size/sort of compressor are you using.? Must be serious pressure/blow with 2.