I have noticed a serious lag from the Zen-fire feed using Mirus compared with the e-Signal version 10.5
Man, your internet connection must suck

No, seriously - where exactly are you seeing a delay in zen-fire (the feed that does not even exist - technically)? Zen-Fire (which is mostly a marketing term - they do not do the technology) can handle a lot more than some dozen symbols - if you have the proper bandwidth.
Or do you use - Ninja Trader, which, being not exactly a stellar application, has - hm - some VERY tupid possible programming issues (especially if you have time and sales open) that SIMPLY may delay the user interface?
How many symbols do you get (i.e. subscribe to)? I am currently in the process of moving my own programming away from crappy NInjaTrader to something I write myself, and in the process also retirng the zen-fire api (towards the real deal - zen-fire does technically not really exist, it is merely a wrapper around another technology).
Here is the news: in this other API (same backend system, I basically use what Zen-Fire used to write their API around - and seriously made some not smart decisions) I can easily grab the data stream of the whole exchange

Including options etc. I was warned, though, that this may be around 30.000 ticks per SECOND on the extreme (note: most is bid/ask changes obviously - complete order book). I can see Ninja crapping out at a miniscule part of that - thanks mostly to some really impressive programming (not in the positive sense).
But this is not the "Zen-Fire" feed crapping out, it is only the front end.