I presume you are shooting Digital? If so the camera's sensor is already filtered, Red/Green/Blue, and will be compositing the sensor readings to make a colour image, even if you have settings suggesting Black & White, which it will make merely from an in-camera conversion.
You'll likely get a more faithful high contrast image, as you hope, shooting digital, 'straight' in colour, no filter, then extracting the mono-chrome red 'layer' from the file in a post-prod package.. with options to tweek contrast in that image layer, or the green and blue, which you can re-merge to get whatever level of contrast you want in resultant B&W image.
Filtering the image entering digi-cam with a red filter, in theory, would mean that the already red-filtered receptors get the light they would, dimmed, the green and blue filtered receptors, nothing at all... but in practice they will get a mute signal, hence you wont get the full saturation of the red-filter, and in conversion to B&W the cameras electrickery will still likely try and use that data. probably amplified some-what, to make the B&W rendition.. hence don't bother pre-fltering, camera already does; Then do it all in post, to get what you really hope for.
If you really want to get the effects of the old masters, though.... use the techniques of the old masters.... go grab a film camera, some pan chromatic film, and use your red filter on that, like they did! ;-)
But as has been said, you need contrast in the sky to start with, before you try boosting it, and if it isn't all that moody, you wont get it... short of compositing a moody sky into your scene in post, as was done in the days of past-masters, under an enlarger with a bit of dodging and burning, before such techniques were automated into HDR merging methods! Which actually may be another way to skin the cat, actually.....
Again ditch the pr-filter; treat it as an HDR exercise; shoot your scene on a tripod, in full-colour Digi, with separate exposures, a couple of stops over and above nominal, then mess with them in post, either extracting red-layers from source files and HRD merging them, or merging colour originals in HDR and extracting red-layer from that... see what you get and go from there.
Other wise, the 'wratten' factor quoted on a filter or its packaging, is a guide to how many stops of light it blocks, and indication of how much to up your cameras exposure settings, over an unfiltered meter reading, either TTL or via separate meter, but it is ONLY a guide. As said, a colored filter doesn't quite pass 'all' its own colour light and block the rest, it blocks most of the other colours, but also some of its own, so how many stops of light it blocks in each colour, and what the ultimate filter factor may be is very situation dependent. Resultant contrast shift more so.
Metering TTL with the filter, may actually get a 'better' exposure, but even without a filter, it's not an exact science! If you have a large amount of bright sky in a scene, you may get a more pleasant, and likely higher contrast, exposure under-exposing a couple of stops anyway; shooting to the histogram, or taking an ambient meter reading with a hand held meter and invercone, even taking some spot-meter readings and picking an average skewed towards shaddow or highlights depending on your preference.
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