For most hams needs the 7300 will do fine, the ultimate channel selectivity is around 110Db which is very good but were the problems will arise is when you place that radio into a BIG antenna farm, this is were that might be an issue or in a multi op station. When I had owned a FTDX3000 and a 7300 at the same time with moderate antennas like a small tribander at 35' and a ZS6BKW at 60' I ran these two radio's side by side during a CQWW phone weekend, the 7300 could pick away at finding a clear spot on 40m at night better than the Yaesu, I used attenuation on both these radio's on the low bands plus no pre amp on the higher bands, its just not needed but I will say that the control flexibility was better on the Yaesu.
Comparing the 7300 to the 7610 is another case were its just that tad better performance of the ADC's and FPGA which just gives that edge in a more competitive operating environment but for every day use they are both great radio's.
As far as the K4 its in the game again, its another knob type SDR, has all the right numbers for an SDR rig but just wait n see on a real review were someone takes the radio home for a week ot two and does some real operating with it, if someone can just walk up and use it and not have to RTFM well ease of use is a plus, another is how easy it is to filter out the guy that just started to call CQ 2Khz away not how great the lab numbers are. I find Icom and Kenwood make the operating ease of use very palatable but Yaesu I feel is not at that level, whoever designed the FTDX101D or even the new FTDX10 just doesn't understand control layout, its almost like someone said wee need this and that feature and just threw it on the front panel with no rime or reason but its all there so this brand there has always been a learning curve. We shall see on the K4, I only had a small amount of time at Orlando to play with the K4 cause they were mad packed but I really didn't warm up to it that fast, there were other rigs which were far easier to use plus I will say it was much nicer that the K3s which I felt was not easy even thou I owned a K3 years back.
Another thing is even if you order one today you maybe be getting it next year so even though its out there delivery times are far away plus by that time I am sure one of the big three from Japan will have something new, we will see.