Different ports handle pool difficulty differently, there is no way your miner would work better/worse just because of that, using high difficulty means fewer shares reported to the pool but every share is worth more, reported hashrate will fluctuate when you use high diff on a slow gear, eventually it will catch up and average out, but it would be pretty normal to see a 100th gear reports 500th and then 5th, but that doesn't change the fact that it's nothing but a 100th gear.

You and the pool want something in between, something reasonable, not too low that submits every share every ms and puts stress on the server, your router, and everything involved, also not something too large, where your miner needs 30 mins to find a share above the set difficulty and gives you all those wired readings and then you don't know what's the real hashrate your miner is getting.

Note that, all of that has exactly no effect on your chances of hitting a block, any share that hits a block with be greater than the difficulty set by any port/pool, but to ensure a smooth operation, always just the ports specified by the pool operator, if it tells you port x is for rental, it really means it's for rental, using it to mine directly could create issues along the way.