After some extensive forum reading, I am down to MSO5074, SDS1104X-E and still maybe HDO1102/4 .
For FPGA work I'd want the 350Mhz 'scope...
And as far as front end noise, is it usable if I say need to look at FPGA 1.1V power rail and check its ripple (5-10mV)?
This is the sort of raw noise level you can expect from an MSO5000:
5 to 10mV of ripple would be clearly visible even with that much noise.
Plus: Ripple will usually be periodic so you can turn on averaging mode and get a huge improvement. eg. This is a 2mV sine wave.
So... it's not ideal, but it's not the end of the world.
FPGA power rail will not be periodic at all... Who told you that?
It will depend heavily on what FPGA is doing at the time, how PDN is designed in a first place and weird interactions between switcher PSU residues, regulation loop, PDN impedance and FPGA current consumption patterns. Actually MSO5000 itself has a problem that you can hear PSU inside with sound modulated by what scopes digital chips are doing at the time...
And that amount of noise, which amounts to more than 25% of signal measured is not fine...
For this job he would be better of buying old DS2000A from Rigol or SDS1000X-E.
Those are both low noise, real 500uV/div designs.
DS2000A also has 50Ω input path and is 300MHz design. It is 2 ch only though..
There are better scopes for that work but more expensive so they do not come into comparison.
MSO5000 would be good for digital part though. It also has better long FFT (similar to SDS1000X-E) than old DS2000A, you could use that to try to extract some info from data...It also have bigger screen.
Like it was said in MSO5000 "good enough" topic, in this price range it is about which tradeoff is acceptable to you.