Mister P, thanks for your kind words, just trying to give my one cent, doing my best in a foreign language and having great time at Iboats. Some side notes :
1-If possible try the size and floor you intend to buy with your 4 HP, if it could be a demo boat, or a good Samaritan boater to lend you one, the better. So to invest well.
2-Planing or not planing will be related to sib pressure, hull drag if it's a slat, Inflatable V, inflatable keel sib, engine 100% operational, driver weight and distribution.
3-A 270 sib has about 1.50 mtr available transon, bow deck space, if placing a tiller extension and moving yourself towards front you will end as a figurehead.
4-An air floor sib is very fast to inflate, low volume, high pressure. Second fastest after a slat floor.
5-Been trying to plane a 270 rib with a 5 HP with no avail whatsoever, not even driving sitting at bow, rib is short and wide, too much hull drag to overcome with my weight.