I tried the Prestige Mids after I gave up on the k90 (same reason as you, too hefty / high swingweight, it's nice for grooving strokes at half pace, at full rally pace you have to prepare early for every groundstroke). I found the Mids a good serving racket, but quite muted overall, and without much feel for volleying, so I moved on quickly.
This was next on my list of sticks to try, if I didn't like the AG100. Looks good on paper.
As for the Dunlops, I'd suggest you try the AG100 before the AG300. The weight difference (on paper) is close to 30g, so if you like the weight and overall feel of the 100 you'll find the 300 too light. I say on paper, because a customisation that I have done (and most people do) on the AG100 is to replace the dunlop hydramax grip for a TW leather grip (I went for the thinner, narrower version) with a Wilson Pro overgrip, which adds about 20g to the handle - and hence the weight of the racket. With that customisation, my AG100s weigh in at 354g and 10 pts headlight, and the swingweight may perhaps have gone fractionally below the 312 of the stock frame. Now, if you look at the specs of the k90, it's 354g and 9 pts. headlight, but with a swingweight of 336. Hence, effectively, a (leather-grip-customised) AG100 is a less hefty clone of the k90 - admittedly, it doesn't feel as solid on groundies, but by the same token if you tend to get caught late with your preparation then it's a lot easier to manoeuvre into a reasonable stroke than the Wilson plank.
If you find the AG100 still too small (head) and heavy, then the AG300 may be a good option - lighter, with a 98 head. It's actually a very customisable racket, you can add lead to the hoop and handle, and bring the weight and balance to whatever suits your game best.
Another racket I tried is the Redondo - I used the 93, but it also comes in a 98 version. It's a traditional / old graphite mould, reasonably heavy but head-light, so very manoeuvrable for S&V, but also not stiff at all so easy on shoulder and elbow. I moved to the AG100, but I liked the Redondos a lot so I kept those frames too.
Good luck with your tests.