If you live in southern Germany 1.25m is sufficient even for the weaker H frequencies. There is one guy on the DF Forum from the Pfalz with that size and he gets them all. Same www.satlex.net north of Munich with a 1.05m Triax TDA110 and an MTI AP8-T2N on a Topfield 4000. Constant reception on 7W, so it is possible. Further north i would recommend to go up to 1.50m, maybe even 1.80m for bad weather.
ape17, do you really get also the Horizontal Frequencies all the time ? Because there are people further South that don't get them. It seems that the receiver and the LNB is of big importance, also the skew of the LNB.
these transponder (Vertikal) are avaiable: 11746; 11823;11861;11938;12130; 11785. The horinzontal transponders are not avaiable, a test with a 1,25m dish was also without any result!! The LNB on the Gibertini 90 cm is an Invacom TWIN 0,3 and the receiver is a Samsung SPRV 801 CI (Clone Topfield PVR 4000).