I haven't scaled my slideshows to 1400x1050, but I see that Photo-to-Movie lets you set a document size before creating a slideshow (and it accepts 1400x1050), and if you export to Quicktime, you can preserve that resolution. Are your three criteria:
- working and output files are 1400x1050 resolution
- allows precise adjustment of transitions (ie, manual)
- be able to see a waveform of the music to assist with transitions?
Those sound likely in Final Cut Pro, but check in that forum or with an expert to see. You may also want to consider your audience and the limitations of the viewing environment to assess whether they will be able to detect the resolution you're striving for (eg, we had very good image quality in a dark theatre using a commercial projecter and screen, 100 feet away, using S-video output from a consumer camcorder).
John