You should leave I/O Interface as SPTI (default setting), as ASPI is only useful for people who can't use SPTI. Also, this problem is completely unrelated to the use of another burner before, as ImgBurn always gets the current configuration.
ImgBurn can't force any burner to write at a specific speed: it'll send the command for the speed you've selected but it's up to the burner to obey or not. Most buners will use the closest available speed to what you've selected, and, in your case, it's 4x.
I 15:08:45 Destination Media Type: DVD-R (Disc ID: TYG03) (Speeds: 4x, 6x, 8x, 12x, 16x)
Has your burner seen a lot of use? Maybe you could try some cleaning kit on it.