I am thinking about running dual jingway(EK,Danger Den,Phobya)in parallel to have good pressure and the pumps can be bought for $70 for the pair.
The set up would be to Y the RES outlet to feed each pump and Y to bridge them back to a single outlet to feed the loop. This would also add Redundancy in case of a pump failing.
2 pumps are usually just fine in a loop together, but it really depends what you plan to do with them and how you setup your loop. Pumps aren't going to fight each other unless you have 2 pumps of different spec and you could encounter some flow issues where the lower flow pump could restrict the higher flow pump, but wouldn't cause damage...just lower flow and restriction.
I've been running my D5 for around 7 years (just an estimate) and it's still going strong.