First let me caution you that SSDR is not as mature as PSDR. There are many features that have not yet been implemented in SSDR that work well in PSDR. Some examples are DSP is much better in PSDR, the 5000 ATU has memories and SSDR doesn't. Once you get past the software differences the 6300/6500 have similar capabilities. I believe the 6500 has a preselector that might help if you are in an area with broadcast stations nearby. I have a 6500 but find that I rarely have more than one slice open. I use a SteppIR antenna and it is only resonant on one band at a time. I could listen to other bands on an antenna that wasn't tuned to it but never seem to find a reason to do it.
Jon (the other one) makes some good points.
I can't quite tell if you are a current 5000 user that is upgrading or how much you have used other's 5000 radios.
I started with a 3000 and the traded up to a 5000 which I still have at the moment. I purchased a 6300 based on the cost factor and the way I generally operate at this point. I was a good fit.
I will say though that I have continued to experience what I call "Slice Envy" (I am trademarking the term so no stealing). As I play with more of the digital modes and with my recent purchase of Pixel receive only loop, I am well aware that I may quickly wish for the additional horsepower and receiver slices the 6500 offers.
Based on your last line about "finding comfort" I would recommend giving into "Slice Envy (TM)" sooner than later and go with the 6500.
Oh, the 6300 is quite capable of displaying it's entire frequency range in a single panafall, similar to cuSDR.
All of the 6000 Series are capable of that. It just has not been added yet.( read a quote from Tim on Flex Radio's website)
If money is not an issue, I would suggest the 6500 since it has a much higher sample rate than the 6300.
But, the guy I bought my 6300 bought a 6500 and he spent time with both and said other than the 4 slice receivers, he could not tell any difference between either receiver. Both were quiet and heard weak signals equally.
Get the one you want and you'll be happy.
And as another poster pointed out, SmartSDR is still a work in progress compared to PowerSDR.
If you can write code, Flex has opened their API's to everyone to experiment with. I have been making a few feeble attempts myself! :-)
1) built in Antenna tuner, which is a $299 option on the 6300. (you will need to add that to your price comparison)
2) XLR Balanced mike input. A very nice option. I use it all the time with my audio mixer, and before that I had my studio mike direct-wired to the XLR input.
3) More flexible Antenna, RX Antenna, transverter and TX relay options etc. on the back panel.
4) Preselector function
5) More flexible preamp options (If you are using a low gain receiving loop on 160, you might want to add some gain with the preamp, which may not be as available on the 6300. I because the 6300 pre-amp has a built in frequency roll-off on the lower bands . . . Tim or others please correct me on this point if I am in error.)
6) Twice the slice and panadapter options.
7) Twice the panadapter width. (I don't use all of it very often, but it has come in very handy in checking the MUF or examining noise sources at my location.)
8) More options for DAX interfacing related to those options.
For most practical purposes, the strength of the receiver and the purity and quality of the transmit audio, digital signals, and CW note are going to be essentially the same.
Look at the data sheets, technical manuals, and back panel layouts and consider if the extras are going to be worth the difference in price in light of your operating style and expectations.
Either way you can't lose. They are both great rigs!
Ken - NM9P
FLEX-6500 & 1500