Right, well the trend among switcher ICs is definitely towards higher and higher switching frequencies and while that can minimize size, it often doesn't because AC losses in windings and core materials increase exponentially with frequency. For example, skin depth in copper at 1MHz is 65um, which is the same as the thickness of
1oz 2oz Cu plating on a PCB and limits the wire diameter to 35 AWG or smaller (if a significant fraction of the current is AC, as in a DCM choke or a transformer). The specific core material used is a lot more important at 1MHz, too - it has to be one of the advanced ferrites such as Ferroxcube 3F4 or TDK/EPCOS PC200, and even then you'll need to limit AC flux swing to 50mT or so to keep losses under control.
And I'm not even mentioning all the knock-on effects you'll have to deal with as a result of even tiny stray Ls and Cs being meaningful at this frequency.
So if you have a choice and you aren't too experienced at smps design - the latter seems to be the case based on the questions you are asking (hey, we all started off at zero knowledge) - then I'd aim for a switching frequency in the range of 100kHz to 400kHz, especially if you want to stick to using off-the-shelf inductors where you might not know the specific ferrite used, and which are invariably wound with a single wire or flat ribbon so there is no accommodation for skin effect.
That said, the IC you had tentatively chosen doesn't require you to design the frequency compensation and feedback network, which I know can appear to be an overwhelming advantage to the neophyte smps designer; resist the temptation! I'm not a huge fan of TI's switcher ICs these days - they seem to be shitting out new TPS part numbers like a refugee with cholera - but an alternate part to consider that is altogether more flexible is TPS61089/610891. It's about $1 more but has adjustable frequency of 200kHz-2.2MHz, an adjustable switch current limit with a guaranteed minimum value of 7.3A, and a minimum input voltage of 2.7V.
Of course, you could also use a much more common controller IC and an external switch, but that might not cost any less overall and be harder to get working so perhaps not the best choice, especially for those new to smps design.
Oh, and a handy site I always recommend is:
http://schmidt-walter-schaltnetzteile.de/smps_e/smps_e.htmlEDIT - removed unused asterisk; fixed plating weight vs. skin depth