As a owner of 1 large sib (Honwave 4m), 1 small rib/sib (Bombard AX500)and a Searider 4m here is my take on it.
As mentioned a 4m+ aluminium floor with 25/30hp engine is bloody heavy to man handle and really only suitable for trailering; even with bravo pump it is a bloody pain to inflate/deflate each time and you will soon get fed up doing this. I had the launching wheels fitted but hauling across sand etc is hard work even for the gf and the i who are both strong and fit - still left us knackered. The launching wheels broke and after two sets took them back and got a refund.
After buying the SR4, i wanted something that i could carry in or on the roof of the car and be on the water within the minimum amount of time....cue Bombard AX500. It has a rigid floor (so technically a rib) and with the Tohatsu 9.8 is a little belter, yes it has the limitations over the 4m sib but it is far more fun and every time i use it puts a bloody big smile on my face. I can carry the engine and boat anywhere i want without killing me and i love the versatility and flexibility it offers without having to worry about tides or slipways.
The beauty of sibs is the ease of launching, low weight and performance and that can achieved with a smaller type boat and 2 stroke engine however go to big and i personally think you will be disappointed considering you already have a Searider.
So as mentioned, i would look at a Aerotec 380 or similar and the largest 2 stroke that can be fitted, comfortably carried or pushed if using wheels. Also get a Bravo or similar electric pump as inflating the thing will goose you before even getting on the water.
I plan to keep the SR4 and the AX, as for me is the perfect combination for what i require.
If you are interested i am selling the 4m Honwave.