I might see if I can make a cable to actually bypass the whole FX loop too (I'm not a fan of FX loops).
I don't know if the loops on the 5150 are much different from that on my 6534+ - I know the 5150 II loop is the same as mine - but I've found the loop to be extremely useful on mine, mainly for noise reduction purposes with the G-String pedal. I really haven't found any downsides to the loop on mine, although I know that some amps (such as the Marshall JVM) can have problems with their loops. I think there may be some effects that have problems in the Peavey loop, but I don't have any in mine. Most of my pedals - and all of them in the loop besides the ISP - are MXR analogue pedals. I don't know if they play nice with digital reverbs etc. I'd suggest giving it a try first. The Peaveys generate a lot of fizz in the preamp section so I found that the noise reduction really needs to go after the preamp.
I used to own a 6505 and I found the preamp generates enough noise to force me to have unnatural settings on my NS2 if I ran it in the loop. I've never used loops and I don't use many effects. My SLO has no loop at all. At most I have a tuner, possibly a wah, maybe a delay, and I run those at the front of the amp and usually on batteries but I do have a good isolated mains supply for them.
Adding a choke will improve the power supply filtering a bit, I'm half way through doing that. I also happen to know from experience which resistors in the preamp can add a LOT of noise. One in particular will be having it's value reduced, which will cut a lot of hiss. The loop being slightly surplus for me, if bypassed, will get rid of 2 valve stages (send and return stage), the associated gain drop/increase in the loop (also boosting noise) and the series resistances in that circuit. I need to check a few things before I try it though but it should just require a jumped wire. The 5150 loop bypass only switches the send and return jack sockets out of circuit. The loop is always passing the signal. There are some more noise reduction tricks too. I'm also careful where I run the gain and I'll be using a 5751 in V1 which should help too.
Compared to the SLO the 5150 is very noisy, has less pushy mids, more fizz, more gain, a poor clean/crunch channel and isn't built as well. BUT... it has that 5150 sound. When I use it I instantly feel like I'm playing with the rig from loads of albums I like... If that makes sense. It's very much a go-to kind of amp for certain styles for a reason. It's based on the SLO100 but it's nowhere near a clone. Just a couple of similarities in the circuit.
