Don't really want meter that cant trust to always to "just work"...
I have a GDM-8251A currently, and like it a lot, just find myself needing higher resolution than that 5 1/2 digit meters can do...
go up another couple hundred and just get a Keysight/Keithley meter...
OK, there's a couple of issues. First is whether you would like all the extra on-board on-screen features that meters like the Siglent SDM3065X (or-SC) or the Keithley DMM6500 offer. Both those have multi-channel scanning (if you buy the -SC in the Siglent or the add-on card for the Keithley) and all manners of logging and graphing software--really cool stuff. Or do you want super-reliable no fuss operation with the scanning and logging features mostly done by PC interface, if at all. I prefer the second just because of how I use the meter. On my main bench meter, I can push the front power button (and one additional button for anything other than DCV) and literally take a reading in one second. Dual display is one additional button and it usually chooses the function I want automatically, if not, it takes two additional seconds. I've never, ever had a 'crash'. So, those features come with the cost of complexity and the occasional glitch.
Second, if you have a GDM-8251A now and like it, what are you looking for as far as resolution and accuracy? The 8251A is perfectly adequate as a bench service meter, etc, but is really not worthy of even being in the 5.5 digit class--it has no high impedance input, very poor accuracy specs relative to other 5.5 digit meters (and in my experience owning one, it barely meets even those specs and has terrible tempco) and is 120,000 count. Not trying to disparage your gear, just pointing out that anything you are considering will be a huge step up, not incremental.
And for 'going pro' and getting a name-brand meter, that might be a good idea. The Siglent gear I do have is pretty good--I'd call it prosumer quality--but it was also at a huge discount to what an equivalent Keysight or Tek instrument would have cost. The DMMs, not so much. If you want to stay near the $700 price point, the Siglent looks good. If you really aren't price sensitive and are willing to stretch, the Keithley DMM6500 and Keysight 34461A look good and have the fancy features, the Fluke 8845A is old but reliable and simple to use. Any of them are available in the just-over-$1K range--and I don't think that is a very large price premium for reputable brands with a long history of quality.